Contingent reward procedures have been found beneficial in improving classroom conduct of ADHD children. Based on the conceptualization of the Premack Principle, a previous single-subject study of an ADHD Autistic child suggested the novel use of physical activity availability as a reinforcer for attentive calmness of the Attention Deficit Hyperactivity Disorder (ADHD) child in a laboratory situation. The present study extended this finding to two older ADHD children in a typical special education classroom. The result is an increase of attentive calmness for the duration of the class for both children. These results suggest the possible use of this special type of reinforcer for general classroom usage in behavioral contingency management programs for ADHD children.